The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known hybrid powertrain architectures include torque-generative devices, including internal combustion engines and non-combustion torque machines, e.g., electric machines, which can transmit tractive torque to an output member preferably through a transmission device. One exemplary hybrid powertrain includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving tractive torque from a prime mover power source, preferably an internal combustion engine, and an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. The electric machines are operative as motors or generators and can be controlled to generate torque inputs to the transmission independently of a torque input from the internal combustion engine. The electric machines may transform engine mechanical power and vehicle kinetic energy transmitted through the vehicle driveline to electrical energy that is storable in an electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain, including controlling transmission operating range state and gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange between the electrical energy storage device and the electric machine to manage outputs of the transmission, including torque and rotational speed.
Known hybrid powertrain systems operate electric machines as motors to generate torque inputs to crank and start the internal combustion engine. This includes executing a key-on engine start event and an autostart event during ongoing vehicle operation. A key-on engine start event can include a cold-start, wherein the internal combustion engine, the electric machine, and/or the electrical energy storage devices are at or near an ambient temperature.
Power limits and electrical power flow capabilities of known electrical energy storage devices are constrained at low ambient temperatures. It is known that magnitude of torque required to crank and start an internal combustion engine increases at lower engine and ambient temperatures, thus affecting cold-starting capability of an internal combustion engine.
Known internal combustion engines include direct-fuel-injection systems having high-pressure fuel systems. A high-pressure fuel system may be limited in the mass of pressurized fuel that is delivered under low power conditions and cold ambient conditions, including during engine cranking events. Engine and operating conditions may require extended crank times to achieve sufficient fuel pressure to fuel the engine. Known direct-fuel-injection systems may employ a second low-pressure fuel pump that operates during cold engine starting events to achieve sufficient fuel pressure to fuel the engine.